On Friday morning, Dr. Yuan called again. Yang Ping called Zhaxi to the office and turned on the speakerphone.
"Professor Yang, the test results for the book pages are out." Dr. Yuan's voice had a restrained excitement. "We found traces of organophosphates on some of the books on the deceased's bookshelf. The concentration isn't high, but they are indeed present. Moreover, we also detected residues of toluene and xylene on the pages of these books."
Yang Ping's breathing paused for a second: "Which books?"
"Mainly those on the second row of the bookshelf, about twenty or so. They're all chemistry books, some are textbooks, and some are monographs. Each one has residues, but the concentration distribution is uneven, with the highest concentration at the edges of the pages and lower concentrations in the middle."
Yang Ping asked, "What about the fingerprint test results?"
